Device and method for using carbon dioxide originating from a combustion process

ABSTRACT

A device for using carbon dioxide originating from the combustion of a byproduct has a preparing unit which is connected to a delivery station for fossil fuels, which has a burner for combusting a byproduct that is released when the fuel is delivered, and an exhaust gas line that is connected to the burner. A depositing device is fluidically connected to the preparing unit via the exhaust gas line, for carbon dioxide. The depositing device is fluidically connected to the delivery station to redeliver fuel via a supply line for carbon dioxide. Such a device allows the production and the subsequent controlled use of carbon dioxide from previously unused byproducts in the production of crude oil. A corresponding method by which carbon dioxide originating from the combustion of a byproduct is used in a controlled manner, in particular as part of a fossil fuel extraction process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2015/054249 filed Mar. 2, 2015, and claims the benefitthereof. The International Application claims the benefit of GermanApplication No. DE 102014204646.7 filed Mar. 13, 2014. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a device for using carbon dioxide that isformed in the combustion of particularly a gaseous by-product, inparticular in the context of producing a fossil fuel. In addition, theinvention relates to a method for using carbon dioxide formed in thecombustion of particularly a gaseous by-product.

BACKGROUND OF INVENTION

The deposits of fossil fuels stored in the ground such as, for example,natural gas, or in particular oil, which are obtainable economicallywith current technology serve as energy reserves in order to cover theconstantly increasing energy consumption of current times. Oil in thiscase is used as one of the most important raw materials for generatingelectricity, as a power fuel for vehicles and means of transport, andalso as a starting material for numerous products of the chemicalindustry.

For oil extraction, it is recovered from subterranean reservoirs. Inthis case, in principle three recovery phases are distinguished. Primaryrecovery denotes the recovery phase in which the fuel is recovered bythe naturally occurring overpressure of the oil, termed the reservoirpressure.

If, in the course of the primary oil recovery, the reservoir pressurefalls, in the framework of the second recovery phase, secondaryrecovery, water or inert gas can be injected using injection probesinstalled by wells, and the reservoir pressure thus increased again inthis manner, up to 40% of the oil present in total can be recovered.

The residual increasingly viscous and dense bituminous oil, however,makes this further recovery difficult. In this case, use is made oftertiary oil recovery (Enhanced Oil Recovery (EOR)). For the tertiaryoil recovery, large amounts of carbon dioxide (CO₂) are required whichare forced at high pressure into the oil reservoirs. The injected carbondioxide dissolves in the oil, swells it and thus lowers its viscosity,in such a manner that the oil can more readily flow in the direction ofthe recovery site or the recovery well, finally be conveyed with the aidof pumps.

Possible sources for the carbon dioxide required for the recovery are,for example, natural reservoirs, exhaust gases of industrial processesor power plant exhaust gases. Since the carbon dioxide that isutilizable from these sources, however, is customarily not present inthe concentration required for oil recovery, a correspondingconcentration is necessary. For this purpose, known methods areavailable, such as physical or chemical absorption, adsorption orseparation by means of selective membranes, which, however, areassociated with high operational costs.

In addition, it is possible to recover carbon dioxide from fossil fuelsby means of the oxyfuel method. In this case, a fuel is burnt with pureoxygen, wherein an exhaust gas is formed, the main constituents of whichare substantially carbon dioxide and steam. The carbon dioxide can thenbe concentrated by condensing the steam. For use in tertiary oilrecovery, the oxyfuel method, however, is possibly not usableeconomically.

In addition, it is necessary to consider that even with a sufficientlyhigh concentration and the required purity of the carbon dioxide, thesites where CO₂-rich exhaust gases or other CO₂ sources are accessibleare customarily spatially far removed from the recovery sites for oilproduction.

The supply of carbon dioxide to the corresponding recovery sites istherefore associated with corresponding additional complexity and highcosts.

SUMMARY OF INVENTION

A first object of the invention is to specify a device that, with thelowest possible operating and capital costs, permits the production ofeconomically usable carbon dioxide.

A second object of the invention is to specify a method which uses theadvantages of the device and thus permits corresponding provision of therequired carbon dioxide.

The first object of the invention is achieved according to the inventionby a device for using carbon dioxide formed in the combustion ofparticularly a gaseous by-product, comprising a treatment unit which isconnectable to a recovery site and having a burner for combustion of theby-product that is released in the fuel recovery and having an exhaustgas line that is connected to the burner, and also comprising a carbondioxide separation device that is flow-connected via the exhaust gasline to the treatment unit. The separation device is in this caseflow-connectable to the recovery site for renewed fuel recovery via afeed line for carbon dioxide.

In a first step, the invention proceeds from the fact that, in thecontext of oil recovery, together with the recovered oil, by-products,in particular gaseous fuel gases, always exit from a recovery well.Since, however, the costs of transporting these, in particular gaseous,by-products and/or treatment thereof usually exceed the expected salesproceeds, the use of the by-products, in particular the fuel gases, ortreatment thereof is usually dispensed with solely for economic reasons.Instead, the by-products produced in oil recovery, in the absence ofpolicy requirements, are usually flared off unused and the resultantpollutant emissions, such as, in particular carbon dioxide emissions,into the atmosphere are accepted.

In a second step, the invention takes into account the fact that theprocesses underlying pollutant minimization, in particular carbondioxide separation, are already part of intensive research in otherfields. For instance, in particular in the case of fossil-fuelled powerplants for generating electrical energy, more and more frequentlyseparation devices are being used that permit a targeted separation ofpollutants and carbon dioxide present in exhaust gases, and thusmarkedly decrease the atmospheric pollution (Post-Combustion CaptureProcess).

In a third step, the invention recognizes that such a separation devicealready tested in power plants is also suitable for use in oil recovery.Owing to the combination with a suitable treatment unit, by-productsthat are produced during oil recovery, and have to date been unused, canbe used in a targeted manner. In other words, the device permits, inparticular, an on-site production and use of carbon dioxide at therecovery site of the oil.

The treatment unit that can be associated with the recovery site, servesin this case first generating a carbon dioxide-containing exhaust gas bycombustion of the by-products. In the separation device that isflow-connected to the treatment unit via an exhaust gas line, the carbondioxide can be separated off from the exhaust gas and fed to therecovery site for subsequent oil recovery. The feed in this caseproceeds via a feed line that represents the flow connection between theseparation device and the recovery site.

Overall, the use of such a device can markedly improve the economicefficiency of the oil recovery process. Since the carbon dioxideseparated off from the combustion exhaust gas, in the ideal case, isproduced directly at the site of use and used for oil recovery, thecosts of providing and transporting carbon dioxide are absent. Inaddition, by the targeted treatment of the exhaust gas from thecombustion of the by-products produced in the oil recovery, whichexhaust gas is not technically utilizable to date, unwanted emissions ofcarbon dioxide into the atmosphere may be prevented or at least markedlydecreased. The recovery site in this case, depending on the recoveryoperation, can have one or more recovery wells and correspondinginjection wells.

Advantageously, a fuel feed line for feeding the by-products isconnected to the burner of the treatment unit. Thus, a fuel gas exitingfrom the recovery site, or from a corresponding recovery well of therecovery site, can be fed to the burner and there burnt with formationof a carbon dioxide-containing exhaust gas.

The combustion proceeds in this case in particular atmospherically, withsupply of air, for which purpose an air feed line for supplyingcombustion air is connected to the burner of the treatment unit. Inparticular, a gas mixer can further be connected into the air feed line,which gas mixer serves for setting the concentration of the carbondioxide in the combustion exhaust gas.

In principle, for separating off the carbon dioxide from the exhaustgas, all methods are usable that have sufficiently high selectivity anda low energy requirement. Thus, in principle, absorption and adsorptionprocesses, or else the use of membranes, would be conceivable.

Particularly, the carbon dioxide is separated off wet-chemically. Forthis purpose, the separation device comprises an absorber for separatingoff the carbon dioxide from the exhaust gas by means of a scrubbingmedium, and also a desorber that is flow-connected to the absorber forreleasing the carbon dioxide from the scrubbing medium. In the absorber,the carbon dioxide is removed from the exhaust gas by absorption in thescrubbing medium. In order to remove the absorbed carbon dioxide fromthe scrubbing medium and thus produce carbon dioxide, the loadedscrubbing medium is fed to the desorber. For this purpose the absorberis expediently flow-connected via a withdrawal line to a feed line ofthe desorber. In the desorber, the absorbed carbon dioxide is releasedfrom the scrubbing medium by thermal desorption and the regeneratedscrubbing medium is fed back to the absorber for repeated absorption ofcarbon dioxide. For this purpose, the desorber is advantageouslyflow-connected via a withdrawal line to a feed line of the absorber.

The desorbed carbon dioxide, after it is separated off, can be used foroil recovery. For this purpose, the desorber of the separation device isparticularly advantageously flow-connected to the recovery site via thefeed line for carbon dioxide. Thus, the carbon dioxide that is releasedcan be used on site for oil recovery. Expediently, the feed line for thecarbon dioxide is connected to the top of the desorber.

In a particularly advantageous embodiment, the exhaust gas line isheat-connected to a steam generator. The steam generator is expedientlyconnected into a steam circuit. The steam circuit, also termedwater-steam circuit, serves for removing heat formed during thecombustion. The hot combustion exhaust gas in this case is conductedpast the steam generator and heats in this case water circulating in thesteam circuit with formation of steam. The exhaust gas itself cools andcan then be fed to the separation device to separate off the carbondioxide that is present in the exhaust gas.

To use the resultant steam, it is, in particular, advantageous when thesteam generator is flow-connected to a steam turbine. In other words,the steam turbine is integrated into the steam circuit. Since, in thecombustion of the exhaust gas, more heat is produced than is originallynecessary for the production of steam, in particular for the productionof heating steam for a reboiler, the steam generator can advantageouslybe designed in such a manner that it is suitable for generating ahigher-grade steam of high pressure which can then be expanded in thesteam turbine and used for generating electrical power.

To generate the electrical power, expediently, a generator is connectedto the steam turbine. The electrical power can then be used to cover theelectrical requirement of the separation device itself. Alternatively,it can be used for compression of the carbon dioxide produced or fedinto the general electric consumer grid.

It is particularly advantageous when the steam turbine in the steamcircuit is heat-connected to the separation device. The steam that isexpanded in the steam turbine to a predetermined pressure andtemperature level can thus be used to support the desorption process.For this purpose, the steam turbine is expediently constructed as acounterpressure turbine. Alternative embodiments of the steam turbineinclude, for example, familiar condensation turbines in combination witha corresponding heating steam take-off at the steam turbine or at thesteam generator.

In an embodiment of the heat connection of the steam turbine to theseparation device in the steam circuit, the steam expanded in the steamturbine is fed via a steam line of the steam circuit to a reboiler. Thereboiler, which is expediently connected to the desorber of theseparation device functions in this case as a condenser for the steamcircuit. Within the reboiler, the steam is conducted through a heatexchanger having scrubbing medium taken off from the desorber andcondensed. The condensed steam can then be fed back to the steamgenerator via a condensate line of the steam circuit that isflow-connected to the steam line, and there, again used for heat removalfrom the combustion exhaust gas and at the same time for operating thesteam turbine.

Expediently, the exhaust gas line is flow-connected to a feed line ofthe absorber of the separation device via a withdrawal line. Thus, thecarbon dioxide present in the combustion exhaust gas, after it is cooledby the steam generator, can be removed from the exhaust gas by anabsorption-desorption process within the separation device, and then fedto the oil recovery. Expediently, in this case, a first substream of 50%to less than 100% of the total combustion exhaust gas is fed to theabsorber.

Particularly, the exhaust gas line is flow-connected to the burner via areturn line. Via the flow connection, a substream of the exhaust gas,after it passes through the steam generator, is fed back to the burner.The recirculation in this case proceeds advantageously via a gas mixerconnected into the air feed line and permits a recirculation of thecombustion exhaust gas around the steam generator. Such a recirculationpermits the targeted setting of the concentration of the carbon dioxidewhich otherwise could only be set via the air excess in the combustion,that is to say via the ratio of the actual amount of air to the amountof air required for stochiometric combustion. The desired high carbondioxide concentration would be ensured in this case only by a slight airexcess. However, with a slight air excess, to ensure a stochiometriccombustion, high combustion temperatures are necessary. Forcorresponding combustion temperatures, at all events, the required hotgas parts are only available at very high costs and would requirecomplex cooling. In addition, at high combustion temperatures, theconcentration of nitrogen oxides in the exhaust gas increases.

Thanks to the recirculation, simple components can be made use of andowing to the lower combustion temperature, unwanted increase in harmfulemissions of nitrogen oxides and carbon monoxide in the combustion canalso be prevented. In other words, owing to the exhaust gasrecirculation, the exhaust gas temperature can be held at a technicallymanageable level, with simultaneously an effective increase in thecarbon dioxide concentration in the combustion exhaust gas.

The fraction of the substream which is reused via the return line forcombustion of the influent gaseous by-product, that is to say the fuelgas, is in this case advantageously in a range from more than 0% to 50%of the total combustion exhaust gas.

It is additionally advantageous when a heat exchanger for preheating thecombustion air is connected into the air feed line. For this purpose,the first substream of the heated exhaust gas, after passage through thesteam generator, is passed via the heat exchanger. The substream and thecombustion air are conducted in heat exchange here, wherein thecombustion air takes up the waste heat of the exhaust gas and ispreheated. The first exhaust gas substream fed to the separation deviceis in this case advantageously precooled to the absorption temperaturenecessary in the absorber.

Advantageously, the scrubbing medium used for separating off the carbondioxide from the exhaust gas is an amino acid salt solution. An aqueousamino acid salt solution, and in particular a potassium-containingaqueous amino acid salt solution is expedient in this case. The use ofin particular an aqueous amino acid salt solution is suitable in thiscase, in particular, since an amino acid salt has a negligibly low vaporpressure and does not vaporize even at high temperatures. As a result,in particular unwanted emissions into the atmosphere are avoided, and inaddition, a decrease in the concentration of the active component of thescrubbing medium is prevented.

The second object of the invention is achieved according to theinvention by a method for using carbon dioxide formed in the combustionof particularly a gaseous by-product, wherein a by-product released froma recovery site in a fuel recovery is fed to a treatment unit, whereinthe by-product is burnt with feed of air in the treatment unit, whereinthe carbon dioxide-containing exhaust gas formed in the combustion isfed to a carbon dioxide separation device, and wherein the carbondioxide that is separated off from the exhaust gas in the separationdevice is fed to the recovery site for renewed fuel recovery.

The carbon dioxide which is produced by means of such a method can beused in a simple and inexpensive manner for oil recovery. By thetargeted utilization of the by-products that are unused to date andarise during oil recovery, in addition, a contribution to climateprotection can be achieved by preventing the carbon dioxide beingemitted into the atmosphere.

Further advantageous embodiments result from the subclaims directed tothe method. Said advantages of the device and advantageous developmentsthereof can be applied as appropriate to the method and developmentsthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Hereinafter, an exemplary embodiment of the invention will be describedin more detail with reference to a drawing.

FIG. 1 shows a device for using carbon dioxide according to anembodiment of the invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 shows a device 1 for using carbon dioxide formed in thecombustion of in particular a gaseous by-product of oil recovery. Thedevice 1 comprises a treatment unit 3 having a burner 5 and a steamgenerator 7. In addition, the device 1 comprises a carbon dioxideseparation device 9 that is flow-connected to the treatment unit 3. Inthe separation device 9, carbon dioxide that is formed in the context ofthe combustion is separated off from the exhaust gas by means of ascrubbing medium. For this purpose, the separation device 9 comprises anabsorber 11 and a desorber 13 that is flow-connected thereto.

The device 1 permits an on-site production and subsequent utilization ofcarbon dioxide in tertiary oil recovery. In tertiary oil recovery, theoil that is to be recovered is produced by injecting carbon dioxide intocorresponding wells of a recovery site 15. In addition to the oil, inthis case, fuel gases that are no longer technically utilizable, that isto say gaseous by-products, are released. Instead of flaring off thesefuel gases as is usual to date, the fuel gas stream is fed via a fuelfeed line 17 to the burner 5 of the treatment unit 3. In the burner 5,the fuel gas is burnt atmospherically with feed of air. The air is fedto the burner 5 via an air feed line 19.

The burner 5 is heat-coupled to the steam generator 7 via an exhaust gasline 21 connected to the burner. The exhaust gas formed in thecombustion is conducted via a heat exchanger 23 of the steam generator7, via which the waste heat formed in the combustion can be taken off.The steam generator 7 is connected into a steam circuit 25, orwater-steam circuit, in which water and/or steam circulate. Thecirculating water is heated in the steam generator 7 with formation ofsteam. In order to utilize the steam, the steam generator 7 isflow-connected to a steam turbine 27. The steam turbine 27 is operatedby means of the steam generated in the steam generator 7. The steam isexpanded within the steam turbine 27 and operates a generator 29 thatprovides electric power which is used for covering the electricalrequirement of the separation device 9 itself.

The steam turbine 27 used for expanding the steam is in the present caseconstructed as a counterpressure turbine. The counterpressure turbine 27expands the steam to a pressure and temperature level required forseparating off the carbon dioxide in the separation device 9. The steamturbine 27 is heat-connected to a reboiler 31 in the steam circuit 25,which reboiler is arranged as bottoms evaporator at the bottom 33 of thedesorber 13. The expanded steam flows from the steam turbine 27 via asteam line 35 of the steam circuit 25 to the reboiler 31. The reboiler31 acts in this case as a condenser for the steam circuit 25. The steamexiting from the steam turbine 27 gives off its heat to the scrubbingmedium circulating in the reboiler 31 and is itself condensed in thiscase. The condensed steam is fed back to the steam generator 7 via acondensate line 37 that is flow-connected to the steam line 35 and atthe steam generator takes up—with cooling of the combustion exhaust gasand formation of new steam—the heat provided in the steam generator 7.The heat withdrawn in the reboiler 31 is used for desorption of thecarbon dioxide from the scrubbing medium in the desorber 13.

In order to separate the carbon dioxide from the exhaust gas, thetreatment unit 3 is flow-coupled to the separation device 9 via theexhaust gas line 21. A first substream 39 of the exhaust gas is in thiscase fed to the absorber 11 via the connection of a withdrawal line 41to a feed line 43 of said absorber 11. In this case, the exhaust gassubstream 39 passes through a heat exchanger 45 which further precoolsthe exhaust gas substream 39 before the entry into the absorber 11. Atthe same time, the combustion air in the air feed line 19 is in this waypreheated before the entry into the burner 5.

Within the absorber 11, the first substream 39 of the exhaust gas, inthe present case 50% of the total exhaust gas stream, is contacted withthe scrubbing medium and the carbon dioxide present in the exhaust gasis absorbed in the scrubbing medium.

The scrubbing medium used is in the present case an aqueouspotassium-containing amino acid salt solution. The loaded scrubbingmedium, for release of the carbon dioxide, flows into the desorber 13,where the carbon dioxide is thermally desorbed. The carbon dioxide istaken off at the top 47 of the desorber, optionally compressed andfinally fed via a feed line 49 to the recovery site 15 for renewed fuelrecovery.

A second substream 51 of the exhaust gas, in the present case 50% of theentire exhaust gas stream, after it passes through the steam generator 7and after corresponding precooling in the context of an exhaust gasrecirculation 53, is fed back via a return line 55 into the burner 7. Inthe exhaust gas recirculation 53, the second substream 51, before theentry into the burner, is further fed to a gas mixer 57, into which thecombustion air also flows via the feed line.

Such an exhaust gas recirculation 53 ensures a sufficiently high carbondioxide concentration in the exhaust gas, which through sole combustionof the exhaust gas with air could only be set via the ratio of theactual amount of air to the amount of air required for stochiometriccombustion. In addition, thanks to the exhaust gas recirculation 53, theexhaust gas temperature may be kept at a technically manageable level.

1. A device for using carbon dioxide formed in the combustion of agaseous by-product, comprising a treatment unit which is connectable toa recovery site for fossil fuel and having a burner for combustion of aby-product that is released in the fuel recovery and having an exhaustgas line that is connected to the burner, and a carbon dioxideseparation device that is flow-connected via the exhaust gas line to thetreatment unit, wherein the separation device is flow-connectable to therecovery site for renewed fuel recovery via a feed line for carbondioxide.
 2. The device as claimed in claim 1, further comprising a fuelfeed line for feeding the by-product which is connected to the burner ofthe treatment unit.
 3. The device as claimed in claim 1, furthercomprising an air feed line for supplying combustion air which isconnected to the burner of the treatment unit.
 4. The device as claimedin claim 1, wherein the separation device comprises an absorber forseparating off the carbon dioxide from the exhaust gas by means of ascrubbing medium, and also a desorber that is flow-connected to theabsorber for releasing the carbon dioxide from the scrubbing medium. 5.The device as claimed in claim 4, wherein the desorber of the separationdevice is flow-connected to the recovery site via the feed line forcarbon dioxide.
 6. The device as claimed in claim 1, wherein the exhaustgas line is heat-connected to a steam generator.
 7. The device asclaimed in claim 6, wherein the steam generator is flow-connected to asteam turbine.
 8. The device as claimed in claim 7, further comprising agenerator which is connected to the steam turbine.
 9. The device asclaimed in claim 7, further comprising a steam circuit of the steamturbine which is heat-connected to the separation device.
 10. The deviceas claimed in claim 7, wherein the steam turbine is constructed as acounterpressure turbine.
 11. The device as claimed in claim 4, whereinthe exhaust gas line is flow-connected to a feed line of the absorber ofthe separation device via a withdrawal line.
 12. The device as claimedin claim 1, wherein the exhaust gas line is flow-connected to the burnerof the treatment unit via a return line.
 13. The device as claimed inclaim 3, further comprising a heat exchanger for preheating thecombustion air which is connected into the air feed line.
 14. The deviceas claimed in claim 4, wherein the scrubbing medium used for separatingoff the carbon dioxide from the exhaust gas is an amino acid saltsolution.
 15. A method for using carbon dioxide formed in the combustionof a gaseous by-product, the method comprising: wherein feeding aby-product released from a recovery site in a fuel recovery to atreatment unit, burning the by-product with feed of air in the treatmentunit, feeding the carbon dioxide-containing exhaust gas formed in thecombustion to a carbon dioxide separation device, and feeding the carbondioxide that is separated off from the exhaust gas in the separationdevice to the recovery site for renewed fuel recovery.
 16. The method asclaimed in claim 15, wherein the carbon dioxide present in the exhaustgas is separated off from the exhaust gas by means of a scrubbing mediumin an absorber of the separation device, and wherein the carbon dioxideis released from the scrubbing medium in a desorber of the separationdevice that is flow-connected to the absorber.
 17. The method as claimedin claim 15, wherein the carbon dioxide that is separated off from theexhaust gas in the separation device is fed to the recovery siteproceeding from the desorber.
 18. The method as claimed in claim 15,wherein the heat that is formed in the combustion is removed via a steamgenerator that is connected downstream of the combustion, and whereinsteam is formed in the steam generator by the heat formed in thecombustion.
 19. The method as claimed in claim 18, wherein the steamformed in the steam generator is expanded in a steam turbine.
 20. Themethod as claimed in claim 19, wherein a generator is operated by meansof the steam turbine.
 21. The method as claimed in claim 19, wherein thesteam expanded in the steam turbine is used for separating off thecarbon dioxide from the exhaust gas in the separation device.
 22. Themethod as claimed in claim 19, wherein a counterpressure turbine is usedas steam turbine.
 23. The method as claimed in claim 16, wherein a firstsubstream of the exhaust gas of the combustion is fed via a withdrawalline to the absorber of the separation device.
 24. The method as claimedin claim 15, wherein a second substream of the exhaust gas of thecombustion is fed via a return line to the combustion of the by-product.25. The method as claimed in claim 23, wherein the first substream ofthe exhaust gas preheats the combustion air before entry into theabsorber.
 26. The method as claimed in claim 15, wherein the scrubbingmedium used for separating off the carbon dioxide from the exhaust gasis an amino acid salt solution.